Recently it has been strictly required that electronic apparatuses, especially portable electronic apparatuses are reduced in volume and body thickness and multi-functionalized, and that each of the portable electronic apparatuses includes in its chassis/body a high density mounted substrate having a plurality of electronic parts but improved in efficiency of heat radiation from the mounted electronic parts.
One of the electronic apparatuses of such type is shown in FIGS. 15-17 as a mobile phone. (See, for example, Patent Document 1 listed below.) As shown in FIG. 15, this electronic apparatus 10 comprises a lower side body 101 including an operation input portion 102 and a voice input portion 103, an upper body 105 including an display panel 106 and a voice output portion 107, and a hinge portion 104 connecting the lower body 101 and the upper body 105 to be able to assume their fold-open and fold-closed positions. The lower side body 101 is constituted by an operational side chassis 101a and a backside chassis 101b. As shown in FIG. 16, the lower side body 101 is provided therein with a substrate 121 designed for performing communication process and input and output control, a key sheet 122 having an elastic sheet portion 122a and a plurality of key tops 122b, 122c, 122d mounted on the sheet portion 122a, and a flexible electrically insulating sheet 123. These constitute a plurality of push button switches 110 operative to be switched in switching state between connected and disconnected in response to depression of the key tops 122b, 122c, 122d(See FIG. 17).
To put it in concrete, the electrically insulating sheet 123 is shown in FIG. 17 by a sectional view. The electrically insulating sheet 123 of embossed key and click type has a set of embossed key portions 123a respectively positioned below the key tops 122b. Each of the embossed key portions 123a is provided on its sphere concave side with a movable contact 126 made of metal spring material and having an arcuate section. In addition, the substrate 121 is provided on its upper side with stationary contacting parts 121a, 121b each facing to the movable contact 126.
On the other hand, the substrate 121 is provided on its underside with a heat generating part 129 such as for example a known power amplifier or the like, while, each of the key tops 122b of the key sheet 122 is provided on its surface portion with a heat radiating layer, not shown clearly in the drawings, mainly made of aluminum and a decorative layer laminated on the surface of the heat radiating layer so as to facilitate heat radiation through the key top 122b. 
[Patent Document 1] JP, 2004-311332, A (Japanese Patent Application Publication No. 2004-311332)